Recently, accompanying improvements in the performances of image forming apparatuses such as digital copiers, integrated digital devices having not only a copying function, but also a function as a printer have been developed and popularized. In such an image forming apparatus, the electric power consumption with respect to the respective functions are different from one another.
On the other hand, as a conventional image forming apparatus (Jpn. Pat. Appln. KOKAI Publication No. 5-313536), an image forming apparatus which has a circuit for detecting electric energy consumed at a fixing unit, and in which abnormal heating of the fixing unit, or the like is detected by the electric power detecting circuit, and an electric power consumption is controlled, has been known.
In the same way, as a conventional image forming apparatus (Jpn. Pat. Appln. KOKAI Publication No. 11-143269), an image forming apparatus which has an electric power detecting circuit using variation in impedance due to the heat of a fixing unit, and on the basis of the detected result, determines electric energy by making an electromagnetic induction heating apparatus vary a frequency, has been known. In the conventional image forming apparatus, it is possible to supply a stable fixing temperature without abnormal heating from the electric power detecting circuit and the induction heating apparatus.
However, in these conventional image forming apparatuses, there is no function of taking into account the electric power consumption of the entire apparatus as a digital multifunction device having many functions. Accordingly, there is the problem that the electric power consumption of the entire image forming apparatus must be taken into account, and by further supplying the surplus power in that case to, for example, a fixing device, the temperature of the fixing device must be maintained to be stable and the time for warming-up must be shortened.